The present invention relates to a system and method for validating coins, and to pay telephones using the system or method. The term xe2x80x9ccoinxe2x80x9d is not limited to coins issued as currency on behalf of Governments, but also covers any other tokens which it may be desirable to identify automatically, such as private currencies circulating within large organizations or telephone call tokens issued by telephone companies.
Coin validation systems are used in a wide variety of machines, such as in turnstiles, automatic vending machines and automatic ticket issuing machines, and pay telephones. A wide variety of methods are known for sensing coins and for processing the outputs of the sensors. For example, input coins may be sensed by their influence on a capacitor or an inductor, they may be detected by optical sensors, and the nature of the material of the coin may be examined by causing the coin to vibrate and examining the nature of the vibrations.
The normal use of inductive sensors is to provide a manner of investigating the nature of the material which an input coin is made from. If the coin passes through the field generated by an inductor, so that the coin affects the inductance of the inductor, a ferromagnetic coin will tend to increase the inductance whereas a diamagnetic coin will tend to decrease the inductance. Additionally, if the magnetic field from the inductor is continually fluctuating, eddy currents generated in an electrically conductive coin will tend to reduce the effective inductance of the inductor. These effects can oppose each other. For example, if a coin is electrically conductive and also ferromagnetic or paramagnetic, then its ferromagnetism or paramagnetism will tend to increase the inductance of the inductor whereas its electrical conductivity will tend to decrease the inductance of the inductor owing to the eddy currents. The relative magnitudes of these opposing effects, and hence the net effect of the coin, will depend on various factors including the frequency of fluctuation of the magnetic field. In general, inductive sensing systems can be divided into xe2x80x9chigh frequencyxe2x80x9d systems, in which the magnetic field oscillates at a frequency of at least 100 kHz, and in which the effect of a coin on the inductance is almost entirely due to eddy currents, and xe2x80x9clow frequencyxe2x80x9d systems in which the magnetic field oscillates at no more than 75 kHz, and in which the magnetic nature of any ferromagnetic coin material has a significant effect on the inductance of the sensor. The magnetic effect of a paramagnetic material to increase the effective inductance and the magnetic effect of diamagnetic material to reduce the inductance are both so small that the effect of eddy currents normally predominates unless the oscillation frequency is very low (less than about 10 kHz).
In high frequency systems the change of the inductance of the sensor can be used simply to detect the presence or absence of a coin at the position of the sensor, or the magnitude of the change in inductance can be measured. The magnitude of the change in inductance will depend, for example, on the degree to which the coin entirely overlaps the coil, the electrical resistivity of the material from which the coin is made, and perhaps to some extent the pattern embossed on the face of the coin. In a low frequency system, the direction of the change in inductance can be used to identify whether a coin is ferromagnetic.
GB Patent No. A-2055498 proposes a system using two coin sensors, each of which is a pair of coils arranged one on each side of the coin path, with one of the coils being an oscillating coil and the other being a receiving coil. In one sensor the coils are about the same size as the height of the coin path, which is considered to be the diameter of the largest diameter coin which passes along the coin path. The oscillating coil of this sensor is energized with a low frequency (e.g., 10 kHz), which is stated to be suitable for discriminating the material of the coin. The other sensor uses relatively small coils (it proposes a range of 10 to 30 mm for the height of the coil), arranged at the top of the coin path and extending down sufficiently that its field interacts with the smallest diameter coin expected in the coin path, but not extending all the way down to the bottom of the coin path. The oscillating coil of this sensor is excited by a high frequency (e.g., 100 kHz). The extent to which the sensor is affected by a coin depends on the degree to which the mass of metal of the coin occupies the area of the electromagnetic field between the coils, and therefore the level of signal received in the receive coil is a measure of coin diameter.
WO Patent No. A-87/00662 proposes a system which is stated to be xe2x80x9chigh frequencyxe2x80x9d although no specific frequency is mentioned. It proposes an arrangement of several coils at different heights above the bottom of a coin path. No dimensions for the coils are given, but it is stated that each sensor is arranged so that it is influenced to some extent by coins whose diameter lies in a region attributed to the sensor, whereas the sensor is not influenced by coins whose diameter lies under this region and is influenced by a maximum extent by coins whose diameter lies above this region. Accordingly, the arrangement of several sensors at different heights provides an arrangement for discriminating coins of different diameters.
GB Patent No. A-2169429 proposes an arrangement in which three inductive sensor coils are used for coin validation. Two of these are placed alongside the coin path, whereas the third is placed across the coin path so that the coin passes through the windings of the coil. It is stated that with the coils placed alongside the coin path, coin discrimination improves with frequency, coil frequencies of 100 kHz and 160 kHz are proposed, and it is stated that the change in impedance of a coil occurs by virtue of skin effect type eddy current being induced by the coil in the coin (at least in respect of a coil alongside the coin path). Of the two coils arranged alongside the coin path, one is arranged so that its diameter is generally (but not always) larger than the maximum diameter of coins that pass along the coin path. It is stated that the whole of the coin under test occludes this coil. The other coil alongside the coin path is disposed on the opposite side of the coin path and is placed offset above the floor of the coin path such that only the upper part of the coin under test occludes it. It is stated that the effect of the coin on the first coil provides a parameter indicative of the size, metallic content and the embossed pattern of the coin. It is not stated what the effect of the coin on the second coil indicates. However, it is stated that the coin of particular denomination, a substantially unique set of effects of the coin on the coils is produced.
GB Patent No. A-2045498 proposes an inductive sensor for detecting coin diameter. This uses an oblong inductor mounted so that the smallest acceptable coin overlaps the lower end of the inductor and the largest acceptable coin does not extend above the upper end of the inductor. The inductor is connected to an oscillator circuit which should oscillate at a high frequency (e.g. above 75 kHz), and the normal oscillating frequency in the absence of a coin is proposed to be 600 to 700 kHz, in order that the oscillating magnetic field penetrates only the surface of the coin under test.
EP Patent No. A-0164110 proposes a system using two sensors, each of which comprises a pair of coils arranged one on each side of the coin path. One coil of each pair is an oscillator coil, connected to an oscillator so as to generate oscillating magnetic fields, and the other coil of each pair is a receiving coil. The frequencies of the magnetic fields are stated to be low enough to cause the magnetic fluxes to pass through the coins, but no particular values for the frequency are proposed. It is proposed that the coin material can be discriminated by measuring the maximum signal obtained from one of the received coils. It is proposed that coin diameter is discriminated by measuring the strength of the signals from the two receiving coils at the point, when the coin is between the two sensors and affecting both of them, when the strengths of these signals cross over. It is stated that the various coils are preferably, but do not need to be, the same diameter as each other, but no other information is given about the diameters of the coils. However, from the drawings of EP Patent No. A-0164110 it appears that it is contemplated that the coil diameter is approximately the same as the diameter of a relatively small coin which is expected to pass along the coin path.
EP Patent No. A-0109057 proposes a system in which a coin is stopped briefly at a testing station, at which point it is between two capacitor plates and adjacent an inductor. No information is given concerning how the effect of the coin on the inductance of the inductor is measured and this is left to the choice of the person skilled in the art. However, it is stated that the inductive sensor is smaller than the smallest diameter coin which is to be identified, and it is illustrated as being position immediately above the floor of the coin path at the position where the coin is held stationary and as being just smaller than the smallest coin.
GB Patent No. A-2096812 proposes a system in which a coin is held stationary next to an inductive sensor, and is subjected to a high frequency signal (greater than or equal to 100 kHz) such that there is substantially no penetration of the signal into the coin, and also subjected to a low frequency signal (e.g., having a frequency in the region 1 kHz to 75 kHz) which penetrates into or through the coin and can be used to provide a measurement of the characteristics of the material of the coin. The device is arranged so that when the coin is held stationary, the distance between the coin and the coil depends on the diameter of the coin. It is preferred that the coil has a diameter which is smaller than the diameter of the smallest acceptable coin.
According to one aspect of the present invention a coin validation system is proposed having at least one inductive sensor the effective field of which is substantially smaller (in the height direction of a coin normal to the coin path) than the diameter of the smallest acceptable coin, and the magnitude of the effect of a coin on the sensor (or on a combination of sensors) is analyzed to distinguish between different coins (that is to say, the sensor is not used simply to detect the presence or absence of a coin). Preferably the size of the effective field is also small in the direction parallel to the coin path, but it is not necessary for the effective field to have the same size in this direction as in the height direction. Preferably the sensor (or at least one of the sensors) is positioned so that the whole of its effective magnetic field is spaced from the top of the largest diameter acceptable coin, and part of the effective field interacts with even the smallest diameter acceptable coin. Thus, the sensor can be used to analyze the construction and composition of the largest diameter acceptable coin, but might act only as a diameter checker on the smallest diameter acceptable coin.
Typically, a coin guide will be provided to guide an input coin along a predetermined coin path past the sensor or sensors. Normally a coin insertion slot is provided, through which coins can be input into the coin guide at the beginning of the coin path. The dimensions of the coin insertion slot will define a maximum diameter and a maximum thickness for the input coin.
This system will respond to the material from which an input coin is made, and can be used both with high frequency oscillating systems (so that it responds to the electrical resistivity of the material) or to low frequency oscillating systems (so that is responds at least in part to the magnetic nature of the material of the coin), although it is preferred to use it with low frequency oscillating systems. This aspect of the invention can be used both in systems where the coin is held stationary while its material is sensed using the inductive sensors and in systems where the coin moves through the field of the inductive sensor and its material is detected as it moves, but it is preferred to use it with systems in which the coin is sensed as it moves.
Owing to the small size of the effective magnetic field, the inductive sensor does not respond to the nature of the material of the coin as a whole, but responds to the nature of the material of a spot on the coin (in the case where the coin is held stationary), or a xe2x80x9cslicexe2x80x9d through the coin (in the case where the coin moves), at a height above the floor of the coin path corresponding to the position of the effective field. Assuming that the composition of the coin is the same at all angles from its center, then the xe2x80x9cslicexe2x80x9d in the case of a moving coin can be considered as a straight line cut through the coin, the cut intersecting the coin diameter normal to the cut at a distance along the diameter from one edge of the coin equal to the height of the effective field of the sensor above the floor of the coin path, although in practice the actual detected slice will follow a curved path as the coin rolls. If the composition of the coin is not the same at all angles around its center, then the pattern of variation of material detected by the sensor will depend on the actual curved slice which passes through the effective field and this will not be the same as the composition of a straight line cut through the coin.
Because the very small effective field size of the inductors allows the sensor to respond to the material of a slice through the coin, rather than responding to the material of the coin as a whole, these sensors can be used to detect coins with holes in the center and coins formed with a central disc of one material at an outer ring of another material. This provides an advantage over sensors of the type where the field is effectively coupled to the entire diameter of the coin, in which case the sensor cannot distinguish between a coin made up of two distinct parts with different compositions and a uniform coin of a material having the same magnetic or electrical properties as average property of the two-part coin.
If a sensor is arranged so that its effective magnetic field is concentrated at a position spaced substantially above the floor of the coin path, the sensor will respond differently to coins of different diameters. In addition to the fact that the sensor will distinguish between a coin large enough to interact with its field and a coin so small that it passes below the effective field, the sensor will distinguish between a bimetallic coin having a relatively small diameter, so that only the outer ring of the coin interacts with the effective field, and a coin having a larger diameter so that both the outer ring and the central disc interact in turn with the effective field of the sensor. Additionally, the sensor will be able to distinguish between a bimetallic coin in which the central disc is just big enough to interact with the effective field of the sensor, and a larger coin in which the central disc extends considerably above the position of the effective field of the sensor. In this case, the curve of a plot of the effect of the coin on the sensor against time will have different shapes for the different coins, with the proportion of the curve showing interaction with the central disc as opposed to interaction with the outer ring being greater for the larger coin.
The effect of a coin on the sensor or sensors may be analyzed by measuring the magnitude of the maximum effect (height of peak of the curve), by measuring the rate of change with time (slope of the curve) of the effect, by measuring the duration of an effect (width of peak of curve) or in any other convenient manner. The various measurements may be combined, e.g., in products or ratios. The shape of the curve of the effect plotted against time may be analyzed using curve fitting techniques. In all cases, the analysis results may be compared with pre-stored reference data to enable a validation decision to be taken. Known xe2x80x9cfuzzy logicxe2x80x9d approaches may be used to take the decision on the basis of more than one analysis result. The validation system may include a teachable neural network for learning the best approach to taking the validation decision.
In addition to the use of a single sensor, it is proposed to use sensing arrangements having multiple sensors, each with small effective fields, arranged at different heights. These sensors can be combined in a wide variety of different ways. For example, sensors at different heights above the floor of the coin path can be arranged at different positions along the coin path, so that at least the largest size of coin will interact with each sensor in turn. Coins of different diameters will give different sets of outputs from the succession of sensors, and such an arrangement can also be designed so as to be effective to distinguish between bimetallic and uniform composition coins of the same diameter. Additionally, two or more sensors may be arranged so that their effective fields are at substantially the same position along the coin path, but are at different heights. This concept may be combined with using sensors whose effective fields are spaced along the coin path, and several sensors having effective fields at different heights may be provided at several different positions along the coin path. The various different sensors may all be coupled to the same detection circuit, or separate detection circuits may be used for some or all of the sensors.
The arrangements using more than one sensor can provide highly effective systems for distinguishing between a wide variety of coins. For example, a sensor can be placed immediately above the floor of the coin path, so that it interacts only with the outer rim of the coin regardless of the coin diameter, and its output can be compared with the output from another sensor placed significantly higher, provided that either the sensors are connected to different detection circuits or the sensors are placed at different positions along the coin path. If the outputs of the two sensors are identical, the coin must have a small diameter such that it only just reaches the higher sensor. A larger diameter bimetallic coin will initially affect the higher sensor in the same way as it affects the lower sensor, as the outer ring of the coin interacts with the higher sensor, and will then affect the higher sensor differently as the central disc interacts with the higher sensor, and will then return to the original manner of interaction as the outer disc again interacts with the higher sensor. A larger diameter coin with a uniform composition will affect the higher sensor in the same manner as the lower sensor but for a longer time.
If several sensors at different heights are arranged at the same position along the coin path and are all connected to the same detection circuit it will not normally be possible to identify the effect of a coin on each individual sensor, and instead the curve of the combined effect on the detection circuit may have a complex shape which is difficult to predict. However, this does not matter provided that the arrangement is such that the overall effect of different coins on the detection circuit is sufficiently different that the coins can reliably be distinguished. It is not necessary to know the effects of a coin on the sensors in order to design a coin validation system to detect the coin, since the system can xe2x80x9clearnxe2x80x9d how to detect a coin by passing samples of valid coins through it while in a xe2x80x9ctrainingxe2x80x9d mode, as is common in the art.
It is at present preferred to connect all the sensors to a single detection circuit, as this reduces the size and cost of the overall apparatus. Additionally, this tends to reduce the amount of computation required in the validation operation in the case where several sensors are positioned at the same point along the coin path, since it is not necessary to analyze the effect of a coin on each sensor individually. This reduces the time required for computation and is advantageous provided that the analysis which is performed is sufficient to distinguish satisfactorily between different coins.
It is presently preferred that the detection circuit, for detecting effect of a coin on an inductive sensor, comprises an oscillator connected to the sensor so that the inductance of the sensor affects the frequency of the oscillator. For example, the sensor may form part of an LC resonant circuit which controls the oscillator frequency. The oscillator frequency may be analyzed in an analysis circuit which measures the oscillator frequency by counting oscillations, and thereby obtains a succession of count values representing samples of the curve of the effect of a coin on the sensor plotted against time. These count values can then be analyzed digitally, e.g., in a microprocessor, in the various ways discussed above.
The size of the effective magnetic field of an inductive sensor can conveniently be defined with reference to a plane of measurement, which is the plane in which interaction between the coin and the magnetic field occurs, that is to say the plane of the coin as it passes along the coin path through the magnetic field. The size of the effective magnetic field can be defined as the maximum distance, in the direction within the plane of measurement but perpendicular to the direction of movement of the coin, between the points where the magnetic field strength falls to 50% of its maximum strength within the plane of measurement. This area will tend to contain the vast majority of the magnetic flux from the inductor which interacts with the coin, and the effect on the inductor of the interaction of the coin with the remainder of the magnetic flux in the plane of measurement is sufficiently small that the effect on the inductor can be regarded as arising substantially entirely from the part of the coin which lies within the area defined by the 50% of maximum field strength in the plane of measurement.
Magnetic flux from the inductor which does not reach the plane of measurement can be ignored, since this flux does not interact with the coin and therefore does not result in any effect of the coin on the inductor. However, it is generally desirable that as much as possible of the magnetic flux generated by the inductor passes through the plane of measurement, as any flux which fails to reach the plane of measurement tends to reduce the sensitivity of the inductor to passing coins.
In a typical case, in which the inductor of a sensor is mounted on one side of the side wall of a coin guide while the coin slides over the other side of the wall, the plane of measurement can be regarded as a plane approximately 1 mm from the face of the inductor. However, this spacing may vary depending on the thickness of the wall.
The size of the effective magnetic field of an inductive sensor is not necessarily similar to the size of the inductor coil in the corresponding direction. The size of the effective field can be influenced strongly by the design and construction of the inductor coil and any core, and may be either larger or smaller than the size of the coil depending on the inductor design.
It is particularly preferred that this aspect of the present invention is used with a frequency of oscillation applied to the inductive sensors which is no greater than 50 kHz, more preferably in the range of 5 to 30 kHz, and most preferably about 10 kHz.
According to this aspect of the present invention there is also provided a method of validating coins, comprising subjecting an input coin to the magnetic field of an inductive sensor which inductive sensor has an effective magnetic field the size of which is no greater than 12 mm (preferably no greater than 10 mm, more preferably no greater than 8 mm, most preferably no greater than 6 mm), and making a validation decision on the basis of the effect of the input coin on the inductive sensor or sensors. The size of the effective magnetic field is defined above with reference to a distance in the direction perpendicular to the direction of movement of the coin. However, it is preferred that the width of the effective magnetic field, defined in a corresponding manner but with respect to a distance in the direction of movement of the coin, is also no greater than 12 mm (preferably no greater than 10 mm, more preferably no greater than 8 mm, most preferably no greater than 6 mm), although it is not necessary for the size of the effective magnetic field and the width of the effective magnetic field to be the same.
This aspect of the invention can also be combined with the use of a capacitive sensor, either at the same position along the coin path as an inductive sensor or at a further position. Separate circuitry can be used to determine the effect of a coin on the capacitive sensor or the same circuitry can be used as for the inductive sensor or sensors.
This aspect of the present invention also provides a payphone using the coin validator, and the above method may be a method of validating coins in a payphone.
In another aspect, the present invention provides a coin validator having a coin guide for guiding input coins along a coin path, and a circuit board attached to or forming at least a part of a wall of the coin guide, the circuit board having a plurality of inductors mounted on it and having one or more conductive tracks formed on it interconnecting the inductors and/or connecting the inductors to other circuit components or to locations where wiring is provided for connection of the inductors to other circuit components, whereby the inductors form inductive sensors for use in sensing input coins in the coin path.
This aspect of the invention also provides a method of mounting inductors for use as inductive sensors in a coin validator, comprising providing a circuit board having a plurality of predefined mounting locations for the inductors and at least one conductive track interconnecting the said locations and/or connecting the said locations to predefined locations for other circuit components or to locations for connection to wiring for electrical connection to other circuit components, mounting the inductors at at least some of the predefined locations for them, and mounting the circuit board in a coin guide defining a coin path for input coins, such that the printed circuit board forms or is mounted to a side wall of the coin path.
This aspect of the present invention is particularly useful for mounting small inductors, such as the very small inductors which may be used to provide the very small effective magnetic fields used in the first aspect of the present invention. The circuit boards for the present aspect may be provided using printed circuit technology, and embodiments of this aspect of the present invention can provide a cheap manner of mounting the inductors used to form inductive sensors while ensuring accurate and repeatable placement of the inductors relative to the coin path. Accurate and repeatable placement of the inductors is important, particularly when the inductors are themselves small, if mass produced validators are to have reliable and consistent performance.
The inductors mounted on the circuit board may be connected in series or in parallel, or to separate detection circuits, or in any combination of these, at the convenience of the circuit designer and the circuit board layout designer. The circuit board may be provided with more locations for mounting inductors than are actually used in a particular case, in which case the unused locations may be left unconnected, or may be shorted, as required by the circuitry to which the inductors are connected.
Further aspects of the invention and optional features are set out in the claims.
The various aspects of the present invention and the preferred and optional features can be combined in a wide variety of arrangements, as will be apparent to those skilled in the art, and the present invention is not limited to the particular combinations of features discussed above or disclosed with reference to the illustrated embodiments.